National Electrical Code Forum
Your Questions Answered
Meet Your Distinguished Experts
Moderator: Lloyd Osborn- Cheyenne, Wyoming
Tom Lichtenstein
Republican Organizer-Chicago, IL
Tim McClintock
NFPA Regional Representative-Wooster, OH
Marcus “Sam” Sampson
Western Section 1st Vice President, CMP 15-St Paul, MN
Vince Saporita
Cooper/Bussmann, CMP 10 & 11, NEC Correlating Committee-St Louis, MO
Phil Simmons
Simmons Electrical Service, CMP 5-East Olympia, WA
Christine Porter
Intertek Field Evaluator, CMP 5-Seatle, WA
Recessed Fluorescent Troffer Securement
1. Do the factory wings that many fluorescent troffers have designed to fold out
over the grid meet the requirements for “securely fastened to the framing”?
Reference:
NEC 410.16(B)
Answer: No, 410.36(B) Requires as bolts, screws, or rivets or Listed clips identified
for use with the type of ceiling framing member and luminaire.
See FLUORESCENT RECESSED LUMINAIRES (IEVV) located on page 174 in the 2012
UL White Book. States Recessed luminaires intended for use in suspended
ceilings and provided with integral clips are marked for use with particular grid
systems.
Separate Clips Listed under Luminaire Fittings (IFFX) on page 187 in UL White Book
Emergency Lights: Unit Equipment
Is it a code violation to have general purpose receptacles on the
same lighting circuit that has required battery backed up emergency
lights
Reference:
NEC® 700.12
2)
Answer: No – 700.12 (in part):
Last paragraph:
• 700.12 General Requirements: Unit equipment in accordance with 700.12(F)
shall satisfy the applicable requirements of this article.
• 700.12(F): Flexible cord-and-plug connection shall be permitted, provided
that the cord does not exceed 900 mm (3 ft) in length.
• 700.12(F): The branch circuit feeding the unit equipment shall be the same
branch circuit as that serving the normal lighting in the area and connected
ahead of any local switches.
3. Is it allowed to use the grounding grid of the pools patio as
the grounding electrode system for a separate structure’s
pool equipment?
Answer: No
Reference: 680.26(B)(2) Equipotential Bonding
and 250.52 Grounding Electrodes
680.26 Equipotential Bonding
(A) Performance. The equipotential bonding required
by this section shall be installed to reduce voltage
gradients in the pool area.
680.26 Equipotential Bonding
(B) Bonded Parts. The parts specified in
680.26(B)(1) through (B)(7) shall be bonded
together using solid copper conductors, insulated
covered, or bare, not smaller than 8 AWG or with
rigid metal conduit of brass or other identified
corrosion-resistant metal.
(2) Perimeter Surfaces. The perimeter surface
shall extend for 1 m (3 ft) horizontally beyond
the inside walls of the pool and shall include
unpaved surfaces, as well as poured concrete
surfaces and other types of paving.
680.26 Equipotential Bonding
680.26 Equipotential Bonding
250.52(A) Electrodes Permitted for Grounding
(1) Metal Underground Water Pipe
in direct contact with the earth for 3.0 m (10 ft)
(2) Metal Frame of the Building or Structure
in direct contact with the earth for 3.0 m (10 ft) or more
(3) Concrete-Encased Electrode
at least 6.0 m (20 ft) encased by at least 50 mm (2 in.) of concrete
(4) Ground Ring
at least 6.0 m (20 ft) of bare copper conductor at a depth not less than 750
mm (30 in.)
(5) Rod and Pipe Electrodes
not be less than 2.44 m (8 ft) in length
(6) Other Listed Electrodes
Man-made…
(7) Plate Electrodes
not less than 0.186 m2 (2 ft2) of surface to exterior soil
(8) Pool perimeter equipotential bonding grid
3. Is it allowed to use the grounding grid of the pools patio as
the grounding electrode system for a separate structure’s
pool equipment?
Answer: No
Generator/ Loading
4. A 3-phase 120/208-volt generator nameplate shows the rating
to be 275KW and 285KVA. The load calculation by the engineer
shows the load on the generator to be 790-amperes. Is this
acceptable?
Reference: Article 445 Generators, 110.3(B)
Answer: There is nothing in Article 445 that limits a generator to
80% of its rating. Therefor it can be utilized at 100% of its
rating. 285,000/(1.732X208) = 791.1 amperes = FLA of
generator. The load on the generator is 790 amperes.
Therefore, this is acceptable.
Grounding & Bonding, More than One Bldg
5. 2011 NEC 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch
Circuit(s) requires that an EGC be installed with the feeder conductors and
bonded to the subpanel in the outbuilding. In addition, a GEC is to be
installed to all available electrodes at the separate structure. If there are no
available electrodes and a ground rod is driven and an appropriately sized
GEC installed, is it required that this ground rod be supplemented as required
in 250.53(A)(2) or can the one ground be considered supplemented by the
main electrode system using the EGC to bond them together
Reference: NEC 250.32; 250.53(A)(2)
Answer: Treat each building or structure as an “Island” so far as grounding
electrode systems are concerned. Two ground rods are required at the
building or structure supplied by a feeder unless a single rod meets the 25
Ohm rule in 250.53(A)(2) Exception.
PVC expansion fittings
6) A 200 ampere, 277/480 volt feeder is installed in 50 feet of
2½", Schedule 80, PVC Rigid Nonmetallic Conduit on the south
side of a steel building. During the winter months, the outdoor
temperature differs by as much as 50 degrees (°F). How much
will the conduit expand in length with this change of
temperature? And would an expansion type of fitting be
required?
Reference:
NEC® 352.44 and Table 352.44
Answer: 1.015 inches, and YES fitting is required
•
•
•
A fitting is to be used whenever the length change is expected to be equal
to or greater than 6mm (1/4”)
Straight runs between anchored points
No difference between Schedule 40 & Schedule 80 conduits
Table 352.44 (in part)
6) continued
Compact Fluorescent Lamps
7. Is it permissible to install compact fluorescent lamps in existing
6-inch recessed luminaires?
Reference:
110.3(B)
Answer: Yes, see Self Ballasted Lamps and Lamp Adapters (OOLR)
on page 278 in the 2012 UL White Book.
The OOLR Guide Information states These products
have been investigated for use in the smaller of a
6- or 8-in. diameter, totally enclosed, recessed
luminaire, if they will physically fit, unless marked
not for use in a totally-enclosed luminaire.
PVC expansion fittings
6) A 200 ampere, 277/480 volt feeder is installed in 50 feet of
2½", Schedule 80, PVC Rigid Nonmetallic Conduit on the south
side of a steel building. During the winter months, the outdoor
temperature differs by as much as 50 degrees (°F). How much
will the conduit expand in length with this change of
temperature? And would an expansion type of fitting be
required?
Reference:
NEC® 352.44 and Table 352.44
Answer: 1.015 inches, and YES fitting is required
•
•
•
A fitting is to be used whenever the length change is expected to be equal
to or greater than 6mm (1/4”)
Straight runs between anchored points
No difference between Schedule 40 & Schedule 80 conduits
GFCI Requirements for Basements
8)
A basement is finished except for the concrete floor which
remains original. Is GFCI protection required for all 120volt
outlets in this area?
GFCI Requirements for Basements
8) A basement is finished except for the concrete floor which remains
original. Is GFCI protection required for all 120volt outlets in this
area?
Reference:
NEC® 210.8(A)(5) & 90.4
Answer:
• 210.8 requires ground-fault circuit-interruption for personnel shall be provided
as required in 210.8(A) through (C).
• 210.8(A)(5) Unfinished basements — for purposes of this section, unfinished
basements are defined as portions or areas of the basement not intended as
habitable rooms and limited to storage areas, work areas, and the like.
• GFCI protection would be an AHJ call for the receptacle outlets located in this
basement. The term “unfinished” first appeared in the 1990 NEC. CMP 2
formulated a panel statement in Comment 2-647 of the 1989 TCR that stated
“Determination of whether a basement is “finished” or “unfinished” is subject to
the authority having jurisdiction”.
9. A hot tub is surrounded by a wooden fence with metal poles
that are within 5’ of the water’s edge.
Do all of the metal poles within the 5’need to be to be bonded
to the equipotential bonding grid?
Reference:
680.26(B)(7)
Answer: Yes
680.26 Equipotential Bonding
(A) Performance. The equipotential bonding required by
this section shall be installed to reduce voltage gradients in
the pool area.
680.26 Equipotential Bonding
(B) Bonded Parts. The parts specified in 680.26(B)(1) through (B)(7)
shall be bonded together using solid copper conductors, insulated
covered, or bare, not smaller than 8 AWG or with rigid metal conduit
of brass or other identified corrosion-resistant metal.
680.26 Equipotential Bonding
(B)(7) Fixed Metal Parts. All fixed metal parts shall be bonded
including, but not limited to,
metal-sheathed cables and raceways, metal piping, metal
awnings, metal fences, and metal door and window frames.
9. Do all of the metal poles within the 5’need to be to be
bonded to the equipotential bonding grid?
Answer: Yes
Circuit Breakers/ Handle Ties
10. Can two outside breakers of adjacent four pole, common trip,
breakers be utilizes as a common trip breaker, for 240 volt loads, if they
are tied with an approved handle tie?
Reference: 240.15(B)(1) & (2)
Answer:
No. 240.15(B)(1) states that “Individual single-pole circuit breakers,
with identified handle ties, shall be permitted as the protection for
each ungrounded conductor of multi-wire branch circuits that serve
only single-phase line-to-neutral loads.” These are not single pole
circuit breakers, therefore, handle ties are not allowed.
Bonding Jumper Required?
11. Is an equipment bonding jumper required between a cable
tray and free standing switchgear when uncoated type MC
cables drop from the tray to the switchgear?
Reference:
NEC 392.60(C)
Answer: Yes, a bonding jumper is required. It is to be sized in
accordance with 250.102.
250.102(C) Supply-Side Bonding Jumper applies if there is no
overcurrent protection on the supply side.
250.102(D) Equipment Bonding Jumper on Load Side of an
Overcurrent Device applies if there is overcurrent protection on
the supply side.
T-Grid Mounting of Outlet Boxes
12) Does the NEC allow a 4” square box for t-grid lighting
fixture branch Circuit conductor to be attached to the t-grid
if a support bracket made for this purpose
Reference:
NEC® 314.22(D)
Answer: Yes - 314.22(D) (in part)
(D) Suspended Ceilings. An enclosure mounted to structural or supporting
elements of a suspended ceiling shall be not more than 1650 cm3 (100
in.3) in size and shall be securely fastened in place in accordance with
either (D)(1) or (D)(2).
(1) Framing Members. An enclosure shall be fastened to the framing
members by mechanical means such as bolts, screws, or rivets, or by the
use of clips or other securing means identified for use with the type of
ceiling framing member(s) and enclosure(s) employed.
Lighting Fixtures and Listing
13. Are all lighting fixtures required to be listed and labeled?
Reference: NEC 410.6
Answer: Yes, see NEC 410.6 which states All luminaires and
lampholders shall be listed. This went into effect in the 2008
NEC. For the 2014 NEC all retrofit kits will also be required to
be Listed.
GFCI Requirements for Vending Machines
14) Is it a violation to install a GFCI receptacle for the vending machine
behind the vending machine indoors in a hallway of a commercial
building?
Reference:
NEC® 210.8 & 422.51
Answer:
• No – it would not be a violation. The change in the 2011 NEC® to require GFCIs
to be readily accessible only includes those under the purview of 210.8.
• 2005 NEC® section 422.51 added requirements for GFCI protection of cord-andplug-connected vending machines.
• 2008 NEC® was revised to include a description of a vending machine, with a
FPN on the applicable product standards.
• 2011 NEC® was revised by was relocating the definition to 422.2
• 2014 NEC® will include a new requirement for accessibility to devices providing
GFCI protection where such protection is specified by an Article 422
requirement.
15. Is NM-B cable
allowed in any areas
of a dwelling unit
that has been
converted to a
dental office?
Reference: 517.10(B)
Answer: Yes
ICC Building Code
SECTION 908
ELECTRICAL
908.1 Special occupancies
Where the occupancy of an existing building or part of an existing building is changed
to one of the following special occupancies the electrical wiring and equipment of
the building or portion thereof that contains the proposed occupancy shall comply
with the applicable requirements of the International Code Council Electrical
(National Electrical Code®)
908.1 Special Occupancies
1. Hazardous locations.
2. Commercial garages, repair, and storage.
3. Aircraft hangars.
4. Gasoline dispensing and service stations.
5. Bulk storage plants.
6. Spray application, dipping, and coating processes.
7. Health care facilities.
8. Places of assembly.
9. Theaters, audience areas of motion picture and television
studios, and similar locations.
10. Motion picture and television studios and similar locations
517.2 Definitions
Health Care Facilities. Buildings or portions of buildings in which
medical, dental, psychiatric, nursing, obstetrical, or surgical care
are provided
Patient Care Area. Any portion of a health care facility wherein
patients are intended to be examined or treated.
517.10 Applicability
(A) Part II shall apply to patient care areas of all health care facilities.
(B) Not Covered. Part II shall not apply to:
(1) Business offices, corridors, waiting rooms, and the like in clinics,
medical and dental offices, and outpatient facilities
517.13 Grounding of Receptacles and Fixed
Electrical Equipment in Patient Care Areas
Wiring in patient care areas shall
comply with 517.13(A) and (B)
517.13 Grounding of Receptacles and Fixed
Electrical Equipment in Patient Care Areas
(A) Wiring Methods. All branch
circuits serving patient care areas
shall be provided with an effective
ground-fault current path by
installation in a metal raceway
system, or a cable having a metallic
armor or sheath assembly.
The metal raceway system, or
metallic cable armor, or sheath
assembly shall itself qualify as an
equipment grounding conductor in
accordance with 250.118.
517.13 Grounding of Receptacles and Fixed
Electrical Equipment in Patient Care Areas
(B) Insulated Equipment Grounding Conductor.
(1) General. The following shall be directly connected to an
insulated copper equipment grounding conductor that is installed
with the branch circuit conductors in the wiring methods as
provided in 517.13(A).
(1) The grounding terminals of all receptacles.
(2) Metal boxes and enclosures containing receptacles.
(3) All non–current-carrying conductive surfaces
15. Is NM-B cable allowed in any areas of a dwelling unit
that has been converted to a dental office?
Answer: YES
Photovoltaic/ Overcurrent Protection
16. Are the conductors from a photovoltaic array required to have overcurrent
protection when they enter a building? What if the modules are AC modules?
Reference: 690.9 and 690.11
Answer: Requirements for overcurrent protection are independent of whether
or not the conductors enter a building. “690.9 (A) Circuits and Equipment.
Photovoltaic source circuit, photovoltaic output circuit, inverter output
circuit, and storage battery circuit conductors and equipment shall be
protected in accordance with the requirements in Article 240.” Overcurrent
protection whether for AC or DC has nothing to do with whether or not the
conductors enter the building. The question may be confusing AFCI
protection, which is not overcurrent protection. Per 690.11, DC AFCI
protection is required where photovoltaic systems are installed on or
penetrate a building
Size of GEC Related to Voltage Drop
17. A 200-amp circuit is increased from 3/0 copper to 500 kcmil
copper to compensate for voltage drop. What size copper
equipment grounding conductor would be required for this
circuit?
Reference:
NEC 250.122(B) increased in proportion to the
increase of the ungrounded conductors
Answer:
500,000 cm = 2.98 (Ratio of increase)
167,800 cm
26,240 cm (6 AWG EGC) X 2.98 = 78,195 cm = 1 AWG EGC
MC cable horizontally run through studs
18) Is it required to maintain 1 ¼” or use a nail plate when
running MC horizontally through shallow metal studs?
Reference:
NEC® 330.17
Answer: No – 330.17 (in part):
330.17 Through or Parallel to Framing Members. Type MC cable shall be
protected in accordance with 300.4(A), (C), and (D) where installed through
or parallel to framing members.
• (A) refers cables & raceways routed through wood framing members
• (C) refers to NM cables and ENT routed through metal framing members
• (D) refers to cables and raceways routed parallel to framing members
HVAC RTU Receptacle
19.
If a rooftop unit comes with a built in GFCI receptacle on
the face
of the unit that comes with the old wet location trim cover. Is it within the AHJ’s
jurisdiction to require an in-use cover and WR type receptacle?
Reference: 90.4, 90.7, 300.1(B), 406.9(B)(1), LZFE pg. 239 UL WB
Answer: Yes and No. AHJ always has the jurisdiction to accept or deny per 90.4.
406.9(B)(1) requires the WR receptacle and the bubble cover for premise
wiring receptacles. However, Listed HVAC equipment, NEC does not apply to
the construction of the RTU, this is governed by the safety standard . See
90.7 and 300.1(B). These products are Listed under (LZFE) on page 239 in
the 2012 UL White Book, evaluated to the Standard for Safety for Heating
and Cooling Equipment, UL 1995. Presently, UL 1995 does not require the a
WR receptacle or a bubble cover. Effective October 2014, Listed HVAC units
with receptacles will have to be WR have a bubble cover or pass the rain test
and the receptacle provided with a separate disconnect. This information
can be found in the UL Question Corner of the latest March April IAEI News
magazine.
Grounding Requirements for PV Systems
20) Is it legal to use the AC equipment grounding conductor as the grounding
electrode conductor for the DC side grounding point in a solar photovoltaic
system?
Reference:
NEC® 690.47(C)(3)
Answer:
•
690.47(C) Systems with Alternating-Current and Direct-Current Grounding Requirements.
Photovoltaic systems having dc circuits and ac circuits with no direct connection between
the dc grounded conductor and ac grounded conductor shall have a dc grounding system.
The dc grounding system shall be bonded to the ac grounding system by one of the
methods in (1), (2), or (3).
•
(3) Combined Direct-Current Grounding Electrode Conductor and Alternating-Current
Equipment Grounding Conductor. An unspliced, or irreversibly spliced, combined
grounding conductor shall be run from the marked dc grounding electrode conductor
connection point along with the ac circuit conductors to the grounding busbar in the
associated ac equipment. This combined grounding conductor shall be the larger of the
sizes specified by 250.122 or 250.166 and shall be installed in accordance with 250.64(E).
•
250.121 new for the 2011 NEC® prohibits an equipment grounding conductor from being
used as a grounding electrode conductor. However that is a general rule (90.3) modified
by 690.47(C)(3).
21. In a 22’ pole light, is it required to connect the auxiliary
grounding electrode conductor going to the lug in the hand hole
to the equipment grounding conductors
by means of a wire nut or split bolt?
Reference: 250.54
Answer: NO
250.54 Auxiliary Grounding Electrodes
One or more grounding electrodes shall be permitted to be
connected to the equipment grounding conductors specified in
250.118…
250.54 Auxiliary Grounding Electrodes
…and shall not be required to comply with the electrode bonding
requirements of 250.50 or 250.53(C) or the resistance requirements
of 250.53(A)(2) Exception
21. In a 22’ pole light, is it required to connect the auxiliary
grounding electrode conductor going to the lug in the hand
hole to the equipment grounding conductors
by means of a wire nut or split bolt?
Answer: NO
Service Entrance/ Feeder Tap
22. I have installed a 200 ampere, 120/240 volt, single phase, rain-tight, meter/main breaker panel with eight breaker spaces and
200 ampere rated, feed-thru lugs on the exterior of a dwelling unit. I have terminated 2/0 aluminum, SER cable on the feed-thru
lugs and ran 20 feet (total wire length) of this cable through a non-insulated basement ceiling and into a 125 ampere main
breaker panel located in the basement. The inspector wrote that the feeder cable has to be rated for 200 amperes. I believe that
I have installed this feeder to meet the requirements of the tap rules of Article 240.21(B)(2) and that the installation should be
approved. Who is correct?
Reference: Table 310.15(B)(16), 310.15(B)(7), Table 310.15(B)(7), Definition of “Tap” in 240.2, 240.21(B)(2)
Answer: The inspector is always right. The ampacity for 75 degree C 2/0 aluminum is 135 amperes, but Table 310.15(B)(7) would
allow 2/0 aluminum to serve a 150 ampere service/feeder if it meets the requirements of 310.15(B)(7). Note that it must
serve the entire building load, so there can be no other loads fed from the 200 ampere panel. So, it looks as if the ampacity
of the cable is adequate. But, now it needs to be protected. I tried using the 25 foot tap rule, but cannot, because the
conductors terminate in a 150 ampere CB which is greater than the ampacity of the conductor, and you can’t round up
when using the tap rules. In this case, going to a 3/0 would have increased the ampacity to 155 amperes, so termination in
a 150 ampere CB would be OK.
Size of GEC to Ground Ring Electrode
23. What is the minimum size copper grounding electrode
conductor allowed to connect to a ground ring that is specified
to be a 250 kcmil cu and the service is a 400A fed with 4-500
kcmil cu
Reference: NEC Table 250.66 and 250.66(C)
Answer: 500 kcmil X 4 = 2,000 kcmil
Table 250.66 requires a 3/0 AWG copper GEC
250.66(C) does not directly apply as the 250 kcmil Ground Ring is
larger than the largest GEC required by Table 250.66,
FPLP installed in wet locations in PVC
24) In a power limited fire alarm system is it a code violation to
install FPLP (which is not listed for wet locations) in PVC conduit
underground from building 1 to building 2?
Reference:
NEC® Art 100 Definitions, 760.3(D), 760.179(D)
Answer: YES - 760.3(D) and 760.179 (in part)
760.3 Other Articles
(D) Corrosive, Damp, or Wet Locations. Sections 110.11, 300.6,
and 310.10(G), where installed in corrosive, damp, or wet
locations.
•FPLP installed in wet locations in PVC
24) continued
760.179 Listing & Marking of PLFA Cables and Insulated
Continuous Line-Type Fire Detectors. (in part)
(D) Type FPLP. Type FPLP power-limited fire alarm plenum
cable shall be listed as being suitable for use in ducts, plenums,
and other space used for environmental air and shall also be
listed as having adequate fire-resistant and low smoke–
producing characteristics.
•
•
Underground locations are wet locations
Cables in wet locations must be a type listed for wet locations
Maximum Number of Smoke Alarms
25.
How does one calculate the maximum number of multiple
single station smoke alarms that can be interconnected in a
building?
Reference:
110.3(B), NFPA 72, (UTGT) Pg. 378 UL WB
Answer:
You don’t calculate the number of smoke alarms
that can be interconnected, you look in the installation
instructions provided with the Listed detectors and NFPA 72 the
National Fire Alarm Code which limits them to 12.
AFCI Requirements for Dwelling Units
26) Is the washer outlet branch circuit in a laundry room required to be
AFCI protected? Is the entire laundry room required to be AFCI
protected?
Reference:
NEC® 210.12(A)
Answer:
• No – 210.12(A) does not include a requirement for laundry rooms.
• 210.12 (A) Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch
circuits supplying outlets installed in dwelling unit family rooms, dining rooms,
living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms,
closets, hallways, or similar rooms or areas shall be protected by a listed arcfault circuit interrupter, combination-type, installed to provide protection of the
branch circuit.
• 2014 NEC®: Revised to expand AFCI protection requirement to kitchens and
laundry areas and to specify AFCI protection is required for branch circuits
supplying outlets and devices.
27. If an electric water fountain uses a GFCI receptacle for
protection, is it required to be readily accessible?
Reference: 422.52; 210.8 & Article 100
Answer: YES
ARTICLE 422 Appliances IV. Construction
422.52 Electric Drinking Fountains.
Electric drinking fountains shall be protected with
ground-fault circuit-interrupter protection.
The GFCI protection may be an integral
part of the fountain, may be provided
at the receptacle for the fountain, or on
the branch circuit feeding the fountain.
210.8 Ground-Fault Circuit-Interrupter
Protection for Personnel
The ground-fault circuit-interrupter shall be installed in a
readily accessible location.
100. Definitions
Accessible, Readily (Readily Accessible). Capable of
being reached quickly for operation, renewal, or
inspections without requiring those to whom ready
access is requisite to climb over or remove obstacles or
to resort to portable ladders, and so forth.
27. If an electric water fountain uses a GFCI receptacle
for protection, is it required to be readily accessible?
Answer: YES
Fire Pump/ Switch Location
28. If we have a 125HP fire pump that is located in another room from
the fire pump control (not within sight), do I need to install another
disconnect for the pump if the fire pump controller disconnect is
lockable? If I do install a disconnect switch, what is the rating of the
switch?
Reference: 695.4(B)(1)(a) General. A single disconnecting means and
associated overcurrent protective device(s) shall be permitted to be
installed between the fire pump power source(s) and one of the
following:
Answer: Not only is the disconnect not needed, per 695.4(B)(1), it is not
allowed. The disconnect at the controller is sized to carry the locked
rotor current of all the permitted motors plus the sum of any other
fire pump auxiliary loads.
Insulating Restrictions
29. Where the utility company installs 1/0 aluminum service
conductors instead of the 4/0 AL that are required per NEC for
a 200 amp service is it compliant to install a 8 AWG GEC per
250.66
Reference: NEC Table 250.66 Note 2
Answer: The conductors installed by the utility would be either a
service lateral or service drop, neither of which are covered by
the NEC. The size of conductors required by the NEC would
require a 4 AWG GEC unless the exception of 250.66(A) applies.
Bonding Low Voltage Enclosures
30) Is it required to ground or bond all metal low voltage
enclosures throughout a commercial building?
Reference:
NEC® 250.96(A), 250.112(I)
Answer – No
250.96 Bonding Other Enclosures. (in part)
(A) General. Metal raceways, cable trays, cable armor, cable sheath,
enclosures, frames, fittings, and other metal non–current-carrying parts
that are to serve as equipment grounding conductors, with or without the
use of supplementary equipment grounding conductors, shall be bonded
where necessary to ensure electrical continuity and the capacity to conduct
safely any fault current likely to be imposed on them.
Bonding Low Voltage Enclosures
30) Continued
250.112(I) Specific Equipment Fastened in Place (Fixed) or
Connected by Permanent Wiring Methods (in part)
(I) Remote-Control, Signaling, and Fire Alarm Circuits. Equipment
supplied by Class 1 circuits shall be grounded unless operating
at less than 50 volts. Equipment supplied by Class 1 powerlimited circuits, by Class 2 and Class 3 remote-control and
signaling circuits, and by fire alarm circuits shall be grounded
where system grounding is required by Part II or Part VIII of this
article.
• Does the system require grounding?
• Are there special requirements such as for Haz Loc installations
or electric signs, etc.?
• If so, the answer may change to Yes
Emergency Lights Battery Back-up
31.
Do emergency lights with individual battery back-up require a test
switch and a charging indicator light? If yes, do they have to be visible??
Reference: FTBR, Pg. 158 UL White Book, UL 924
Answer:
Yes and Yes. Listed under Emergency Lighting and power
Equipment (FTBR), see pg. 158 in the 2012 UL White Book.
The Standard for Safety for Emergency Lighting and Power Equipment UL 924.
requires equipment incorporating storage batteries and battery-charging
means shall provide audible or illuminated visible indicator(s) detectable to
facility occupants without the need to adjust or remove any equipment
covers or parts they also need a test switch or provision to connect a test
switch (which can be mounted remote from the equipment, for easier
access).
GFCI Breaker Requirements
32) The 2-pole 50-amp GFCI breaker for a hot tub is installed in the
disconnect 6 feet from the tub. It is a 240-volt 3-wire hot tub. Is a
neutral required to be brought to the disconnect for the reference of
the GFCI breaker? Or can the factory white neutral reference from
the breaker be terminated on the equipment ground bar?
Reference:
NEC® 680.44 & 110.3(B)
Answer:
• 680.44: specifies the outlet(s) that supplies a self-contained spa or hot tub,
a packaged spa or hot tub equipment assembly, or a field-assembled spa or
hot tub shall be protected by a ground-fault circuit interrupter.
33. Where conduit is required for life safety & critical branch
circuits, is it a violation to use factory fixture whip taps for
the 6’ termination to a 2’x4’ emergency light?
517 Part III Essential Electrical System
517.30(B) (2) Emergency Systems. The emergency system
shall be limited to circuits essential to life safety and critical
patient care. These are designated the life safety branch and
the critical branch.
517.30(C)(3) Mechanical Protection of the
Emergency System.
The wiring of the emergency systems in hospitals shall be
mechanically protected. The following wiring methods shall
be permitted:
(3) Listed flexible metal raceways and listed metal sheathed
cable assemblies in any of the following:
a. Where used in listed prefabricated medical headwalls
b. In listed office furnishings
c. Where fished into existing walls or ceilings, not otherwise
accessible and not subject to physical damage
d. Where necessary for flexible connection to equipment
33. Where conduit is required for life safety & critical branch
circuits, is it a violation to use factory fixture whip taps for
the 6’ termination to a 2’x4’ emergency light?
Answer: NO
Sizing Motor Circuits/ Fuse, EGC, and Conductors
34. A 100 hp, 3-phase, 480 volt motor is fed with #2/0 AWG, Type THHN/THWN, copper conductors
protected with Type Non-400 ampere fuses and a #6 AWG copper EGC. Are the motor circuit conductors,
EGC, and fuses properly sized?
Reference: Table 430.52 (and Exception No. 1), 240.6), Table 430.250, 430.22, Table 310.15(B)(16),
250.122, and Table 240.122.
Answer: From Table 430.52 a non-time delay fuse can be sized as high as 300% of FLA, which is 124
amperes from Table 430.250. 3 X 124 = 372 amperes. Exception No. 1 allows the next standards size,
which 240.6 shows as a 400 ampere fuse, which agrees with the question. However, the fuse in
question is only a 250 volt fuse, so it would be a violation of 110.3(B) to use the 250 volt fuse on a 480
system. An NOS 400 fuse would be required for this application. 430.22 requires that the motor
circuit conductor have an ampacity of at least 1.25 X 124 = 155 amperes. Table 310.15(B)(16) shows a
2/0, 75 degree C conductor to have an ampacity of 175 amperes. Table 250.122 would indicate that a
3 AWG conductor is adequate for the EGC, so the 6 AWG conductor would also be in violation.
GEC Connection to Ufer GEC
35. Why is a UFER connection required to be accessible?
Reference: NEC 250.68(A) Exception
Answer: The connection is not required to be accessible due to the
nature of the connection inside poured concrete.
Bushing on RMC nipple?
36) I installed a short rigid nipple out the back of a panel to
an LB that has a 5’ length of EMT to a disconnect switch for
an AC unit. It only has #10 copper wires in the conduit and
the inspector wants a bushing on the inside of the panel. Is
he correct?
Reference:
NEC®310.4(G) and 344.46
Answer - No unless fitting or raceway does not provide smooth edge
310.4(G) Insulated Fittings. (in part)
Where raceways contain 4 AWG or larger insulated circuit conductors,
and these conductors enter a cabinet, a box, an enclosure, or a
raceway, the conductors shall be protected by an identified fitting
providing a smoothly rounded insulating surface, unless the
conductors are separated from the fitting or raceway by identified
insulating material that is securely fastened in place.
Bushing on RMC nipple?
36) Continued
310.4(G) Exception: Where threaded hubs or bosses that are
an integral part of a cabinet, box, enclosure, or raceway
provide a smoothly rounded or flared entry for conductors.
344.46 Bushings. Where a conduit enters a box, fitting, or
other enclosure, a bushing shall be provided to protect the
wires from abrasion unless the box, fitting, or enclosure is
designed to provide such protection.
•
•
If the nipple is listed, it is required by UL 6 to provide the
smooth edge, and would meet the requirement in 344.46.
If the nipple was manufactured in the field then it would be
up to the AHJ to determine if the nipple provides a smoothly
rounded edge for the conductors to pass over.
Grounding Lug to Painted Box
37.
I have a junction box that is 1/16th of an inch thick that is
painted. I drilled and tapped that box for a 10/32 screw for
bonding the box. Do I need to remove the paint or will the thread
contact be sufficient for making contact between the lug and the
box?
Reference:
250.12
Answer:
Yes, you need to remove the paint. 250.12 states
Nonconductive coatings (such as paint, lacquer, and enamel) on
equipment to be grounded shall be removed from threads and
other contact surfaces to ensure good electrical continuity or
be connected by means of fittings designed so as to make such
removal unnecessary.
Ground Bushings
38) Are ground bushings listed for a choke on the GEC when installed in a ferrous
raceway?
Reference:
NEC® 250.64(E) & 250.92(B)
Answer:
• 250.64(E) …Ferrous metal enclosures that are not physically continuous from
cabinets or equipment to the grounding electrode shall be made electrically
continuous by bonding each end of the raceway or enclosure to the grounding
electrode conductor.
• Bonding methods in compliance with 250.92(B) for installations at service
equipment locations and with 250.92(B)(2) through (B)(4) for other than service
equipment locations shall apply at each end and to all intervening ferrous
raceways, boxes, and enclosures between the cabinets or equipment and the
grounding electrode.
• Grounding bushings are Listed under Grounding and Bonding Equipment, (KDER)
• These bonding connections are necessary so that the ferrous raceway does not
create an inductive choke on the grounding electrode conductor. By virtue of the
bonding connection, there is no choke.
39. Is it compliant to run health care facility cable through
PVC in the concrete floor as long as it is not slab on grade
for dental chair receptacles?
Reference 517.13
Answer: Maybe
517.13 (A) Wiring Methods
The metal raceway system, or metallic cable armor, or
sheath assembly shall itself qualify as an equipment
grounding conductor in accordance with 250.118.
300.5(C) Underground Cables Under Buildings
Underground cable installed under a building shall be in a
raceway.
Exception No. 2: Type MC Cable listed for direct burial or concrete
encasement shall be permitted under a building without
installation in a raceway in accordance with 330.10(A)(5) and in wet
locations in accordance with 330.10(A)(11).
330.10 Uses Permitted
(A) General Uses. Type MC cable shall be permitted as follows:
(1) For services, feeders, and branch circuits.
(2) For power, lighting, control, and signal circuits.
(3) Indoors or outdoors.
(4) Exposed or concealed.
(5) To be direct buried where identified for such use.
(6) In cable tray where identified for such use.
(7) In any raceway.
(8) As aerial cable on a messenger.
314.3 Nonmetallic Boxes
Nonmetallic boxes shall be permitted only with open wiring on
insulators, concealed knob-and-tube wiring, cabled wiring methods with
entirely nonmetallic sheaths, flexible cords, and nonmetallic raceways.
Exception No. 1: Where internal bonding means are provided between all
entries, nonmetallic boxes shall be permitted to be used with metal
raceways or metal-armored cables
330.40 Boxes and Fittings
Courtesy Thomas & Betts
Fittings used for connecting Type MC cable to boxes, cabinets,
or other equipment shall be listed and identified for such use.
39. Is it compliant to run health care facility cable through PVC in the
concrete floor as long as it is not slab on grade for dental chair
receptacles?
Answer: Maybe, if the MC cable can be properly terminated to a listed
box or assembly at or beneath the dental chair
Sizing Motor Circuits/ Use of the Tables
40. When determining the Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit
and Ground-Fault Protective Device using Table 430.52, do I use the motor amperages shown
in Tables 430.247 through 430-250 for all type of motor applications or the nameplate rating
on the motor(s)? and why?
Reference: 430.6(1) Table Values. Other than for motors built for low speeds (less than 1200
RPM) or high torque, and for multi-speed motors, the values given in Table 430.247, Table
430,248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of
conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault
protection, instead of the actual current rating marked on the motor nameplate.
Answer: Use the tables for all but low speed, high torque and multi-speed motors. Tables are
used because motors need to be changed out at times and the branch circuit components
need to be large enough to handle the new motor that is being installed to replace the old
motor. If motor nameplate were used and a very high efficiency motor were installed the
first time, the motor branch circuit components might not be rated high enough if a
standard motor were installed in place of the high efficiency motor.
Support Pillars Acceptable as Ufer GEC?
41. Can the concrete pillars used to support a manufactured home
be used for the UFER grounding electrode?
Reference: NEC 250.52(A)
Answer: Probably not if the pillars are installed in the usual
manner, that is, from concrete blocks on the earth surface.
To qualify, a pillar would need to meet the description of a
grounding electrode in 250.52(A).
MC and outlet boxes in raised floor of IT room
42) For power distribution units (PDU’s) inside a room
designated “information technology” with field installation
using MC to 4plex receptacle boxes under the floor, is it
required to secure and support the boxes and wiring methods
as stated in 645.5(E)(2)? Or, would this installation meet the
requirements in 645.5(F)?
Reference:
NEC® 645.5 (E)(2) and 645.5(F) and 300.11
Answer: Possibly
•
•
•
If the assembly is not listed as IT Equipment or for IT Equipment the MC
cable and boxes must be secured in place in accordance with 300.11.
300.11 requires them to be fastened in place without using ceiling/floor
support wires as the means of support.
If the assembly is listed as IT Equipment or for IT Equipment the assembly
is not required to be secured in place.
PV Inverters with AFCI Protection
43.
Since there is only one inverter that is third party listed as
being arc-fault protected, should the requirements of NEC 690.11
be enforced for all inverters therefore only approving 1 type that
has many restrictions? IE.. Only 3-5kws are listed?
Reference:
690.11, 90.4, (QIDC) Pg. 325 UL WB
Answer:
Actually up to 11 KW are Listed for SMA Solar under
the product category PHOTOVOLTAIC DC ARC-FAULT CIRCUIT
PROTECTION (QIDC) located on page 325 in the 2012 UL White
Book. If there aren’t sizes available for an installation under
90.4 the AHJ under special permission may permit products
that complied with the previous version of the Code.
Aircraft Hangars
44) In a small aircraft hanger where the aircraft has its’ fuel tanks in its’
wings is it allowed to have electrical outlets on the side walls by the
wings for servicing the aircraft?
Reference:
NEC® 513.3 & 513.4
Answer:
• Yes – see section 513.3 & 513.4
• 513.3 Classification of Locations:
(A) Below Floor Level – Class I, Division 1 or Zone 1
(B) Areas Not Cut Off or Ventilated. The entire area Class I, Division 2 or Zone 2
location up to a level 18 in. above the floor.
(C) Vicinity of Aircraft.
513.3(C) Vicinity of Aircraft:
(1) Aircraft Maintenance and Storage Hangars. The area within
1.5 m (5 ft) horizontally from aircraft power plants or aircraft
fuel tanks shall be classified as a Class I, Division 2 or Zone 2
location that shall extend upward from the floor to a level 1.5 m
(5 ft) above the upper surface of wings and of engine enclosures.
Aircraft Hangars
44) In a small aircraft hanger where the aircraft has its’ fuel tanks in its’
wings is it allowed to have electrical outlets on the side walls by the
wings for servicing the aircraft?
513.4 Wiring and Equipment in Class I Locations.
Requires all wiring and equipment installed in or operating within Class I
locations defined in 513.3 are required to meet the applicable provisions of
Article 501 or Article 505 for the division or zone in which they are used.
Attachment plugs and receptacles in Class I locations shall be identified for
Class I locations or shall be designed such that they cannot be energized while
the connections are being made or broken.
45. In an operating room that has been identified as a
“wet procedure location” can a regular receptacle
trim plate be used?
Reference: 517.19(A)
Answer: YES
517.2 Definitions: Critical Care Areas
Those special care units, intensive care units, coronary care units,
angiography laboratories, cardiac catheterization laboratories, delivery
rooms, operating rooms, and similar areas in which patients are
intended to be subjected to invasive procedures and connected to
line-operated, electro-medical devices.
517.2 Definitions: Wet Procedure Locations
Those spaces within patient care areas where a procedure is performed and
that are normally subject to wet conditions while patients are present.
These include standing fluids on the floor or drenching of the work
area, either of which condition is intimate to the patient or staff.
517.19 Critical Care Areas
(A) Patient Bed Location Branch Circuits
Emergency system receptacles shall be identified and shall
also indicate the panelboard and circuit number supplying them.
2014 NEC 517.19(C) (new)
(C) Operating Room Receptacles.
(1) Minimum Number and Supply.
Each operating rooms shall be
provided with a minimum of
thirty six receptacles
45. In an operating room that has been identified as a “wet procedure
location” can a regular receptacle trim plate be used?
Answer: YES
Tap Rules/ No Rounding up
46. Is it permissible to use 240.4(b) and round up to the next standard
size over current device on a feeder tap? Example; Can 23 feet of 500
kcmil, Type THHN/THWN copper conductors be tapped off of a 1200
ampere feeder and terminated on a 400 amperes main breaker in a
subpanel?
Reference: 240.21(B) Feeder Taps. Conductors shall be permitted to be
tapped, without overcurrent protection at the tap, to a feeder as
specified in 240.21(B)(1) through (B)(5). The Provisions of 240.4(B)
shall not be permitted for tap conductors.
Answer: No. Ampacity of 500 kcmil is 380 amperes, so it cannot be used
to terminate into a 400 ampere main breaker for either the 10 foot
tap or the 25 foot rule.
Use of Dusttight J-Boxes on Class II, Div 1 Areas
47. Are dusttight “Hoffman type” junction boxes with Meyers Hubs listed for
use in a Class II Division I location approved for use in a Class II, Division I
location as a pull through only box when sized correctly even though the box
is not identified for use in a Class II location, but listed dusttight only?
Reference: 502.10(A)(4) (Class II, Div. 1) Fittings and boxes shall be provided
with threaded bosses for connection to conduit or cable terminations and
shall be dusttight. Fittings and boxes in which taps, joints, or terminal
connections are made, or that are used in Group E locations, shall be
identified for Class II locations.
Answer: A pull box without “taps, joints, or terminal connections,” is acceptable
in the Class II Division 1 area if dusttight.
Show window at a Bank?
48) Where a freestanding bank is built having about 75% full
length windows mostly for security reasons. Is it required to
have the contractor install show window receptacles?
Reference:
NEC® 100 (Definitions) and 210.62
Answer Maybe
Show Window. Any window used or designed to be used for the display of goods
or advertising material, whether it is fully or partly enclosed or entirely open at
the rear and whether or not it has a platform raised higher than the street floor
level
210.62 Show Windows. At least one receptacle outlet shall be installed within 450
mm (18 in.) of the top of a show window for each 3.7 linear m (12 linear ft) or
major fraction thereof of show window area measured horizontally at its
maximum width
•
•
Will they use reader boards, or other signage in the
windows?
Do they advertise using the windows?
Cord Connected Water Heater
49.
Can a 30-amp water heater use a cord connector and
receptacle as the disconnecting means?
Reference:
110.3(B),(KSDT) Pg. 235 UL White Book, UL 174
Answer:
No, see Household Water Heaters, Storage Tank
(KSDT) which states that these water heaters are intended for
household use and permanent connection to the supply source
in accordance with the NEC.
UL 174, permits only small capacity water heaters (5 gal. or less)
to be cord and plug connected.
Sunroom AFCI Requirements
50) Why are sunrooms specifically listed to be AFCI protected but not an
enclosed porch or patio?
Reference:
NEC® 210.12(A)
Answer:
• 210.12(A) Dwelling Units. All 120-volt, single phase, 15- and 20-ampere branch
circuits supplying outlets installed in dwelling unit family rooms, dining rooms,
living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms,
closets, hallways, or similar rooms or areas shall be protected by a listed arcfault circuit interrupter, combination-type, installed to provide protection of the
branch circuit.
• 210.52(A) General Provisions. In every kitchen, family room, dining room, living
room, parlor, library, den, sunroom, bedroom, recreation room, or similar room
or area of dwelling units, receptacle outlets shall be installed in accordance with
the general provisions specified in 210.52(A)(1) through (A)(3).
• IRC: Sunroom Addition: A one-story structure added to an existing dwelling with
a glazing area in excess of 40 percent of the gross area of the structure’s exterior
walls and roof.
National Electrical Code Forum
Your Questions Answered
Meet Your Distinguished Experts
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Electrical Engineer-Ft Collins, CO
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Schneider Electric-, CMP 10, Lexington, KY
Chuck Mello
Underwriters Laboratories, CMP 5-Milwaukie, OR
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Western Section President, CMP 6-St Louis, MO
Junction Box Size
51. What is the minimum size of junction box that can be installed
to enclose a power distribution block that measures 6” x 6” and has
two parallel 3/0 AWG copper conductors per phase terminated on
both sides of the block?
Reference: NEC 314.28(E) with 314.28(A)(2) and Table 312.6(A)
Answer: NEC 314.28(E) permits power distribution blocks in boxes
over 100 cubic inches with wiring handling, routing, and
termination restrictions per 312.6. Table 312.6(A) requires
minimum bending space of 4 inches for the #3/0 conductors.
With the 6 inch power distribution block and with conductors
terminated at both sides, the minimum width of the box would
be 6+4+4 = 14 inches. Also note that dimensions must meet
installation instructions for the power distribution block.
Water Pipe Bonding Methods
52. Can I bond the waterline to a sub panel ground bar and not at the main
panel if the incoming waterline is plastic and the house waterline is copper?
If so, what size wire do I need to bond it with if I’ve fed the house with 4/0
aluminum?
•
Reference; 250.104(A)(1)(2)(3)
•
No, (1) states the water line must be bonded to the service equipment
enclosure, the grounded conductor at the service, the grounding
electrode conductor where of sufficient size, or to one or more
grounding electrodes used.
•
#(2) and #(3) do not apply to the installation described.
•
The bonding conductor is sized per 250.66 (4 AWG cu. Or 2 AWG al.)
Question #53
AFCI Protection – A Proven Safety Device.
•
550.25 states that AFCI protection is required and shall comply
with 210.12. Why then do these leave the factory without the
AFCI protection installed in the panels?
Answer: NO. Title 24 HUD 3280.801 Scope.
(a) Subpart I of this part and Part II of Article 550 of the National
Electrical Code (NFPA No. 70–2005) cover the electrical
conductors and equipment installed within or on manufactured
homes and the conductors that connect manufactured homes to
a supply of electricity.
Question #53
AFCI Protection
Answer Continued: (b) In addition to the requirements of this
part and Part II of Article 550 of the National Electrical Code
(NFPA No. 70–2005), the applicable portions of other Articles of
the National Electrical Code must be followed for electrical
installations in manufactured homes. The use of arc-fault
breakers under Articles 210.12(A) and (B), 440.65, and 550.25(A)
and (B) of the National Electrical Code, NFPA No. 70–2005 is not
required. However, if arc-fault breakers are provided, such use
must be in accordance with the National Electrical Code, NFPA
No. 70–2005. Wherever the requirements of this standard differ
from the National Electrical Code, these standards apply.
Question #54
Fire Pumps
If I have a separate underground service for a fire pump entering
the fire pump controller at the nearest point of entry and the
controller has a disconnecting means built into it (they are all
service rated by code), do I need a additional disconnecting
means ahead of the controller?
Question #54
Fire Pumps
•
•
•
Answer: 2011 NEC: An additional disconnect means is not required.
The connection being described is considered a direct source
connection per 695.4(A). See below. Article 695 permits fire pump
source connections to be either direct or through a disconnecting
means (695.4(B)).
695.4(A) Direct Connection. The supply conductors shall directly
connect the power source to either a listed fire pump controller or
listed combination fire pump controller and power transfer switch.
Note: Fire pumps are typically considered three wire motor loads so
be sure the fire pump controller is ordered with a neutral if installed
on a grounded system. NEC 250.24(C) requires the grounded
conductor be brought to the service equipment
Size of Grounded Service Conductor
55. What would be the minimum size of grounded
service conductor that would be required for an
industrial facility with a 2000 ampere service consisting
of 5 parallel runs in 5 conduits of 600 kcmil Type THWN2 copper conductors? (there are no neutral loads on the
system).
Size of Grounded Service Conductor
Answer - Based on the information in the question the minimum
required size would be 1/0 copper or 3/0 aluminum in each
raceway. Even though there are no phase to neutral loads from
the service, 250.24(C) would require the installation of grounded
service conductors (neutrals) to the service equipment. Again
since there are no neutral loads, then calculation of neutral
conductor size from 220.61 would not be required. Section
250.24(C) does specify a minimum sizing in accordance with
(C)(1) or (C)(2) for either single raceway or multiple raceways
respectfully. With multiple raceways 250.24(C)(2) would require
the size be based on the size of the ungrounded conductors in
each raceway using Table 250.66 and not smaller than 1/0 AWG.
Main
Power Feeder
Paralleled?
56. Is it permissible
to utilize/ Table
310.15(B)(7) and install two
parallel runs of 4/0 aluminum SER cable for a 400 ampere
main power feeder for a single family dwelling?
Reference:
NEC 310.15(B)(7)
Answer: No, this section requires that the conductors be the main
power feeder (not feeders)
•
A 400 ampere service requires 400 kcmil copper or 600 kcmil
aluminum as provided in the Table 310.15(B)(7).
Disconnect Access
57. An RTU is placed on a metal frame for weight dissipation &
built up to where the controller and the breaker (disconnect) is
now 8’ AFF. Is it required to install a working platform 30” x 36” or
is a ladder to access and service the unit NEC compliant using the
exception to 404.8 exception (2) & 240.24(a)(4)
Reference:
NEC 404.1 with 404.8, Exception No. 2
Answer: The circuit breaker disconnect location for the RTU is
governed by NEC Article 404 per NEC 404.1. With the
disconnect mounted at the elevated RTU equipment, access
by portable means (ladder) is allowed by NEC 404.8, Exception
No. 2 in lieu of a service platform.
GFCI PROTECTION
58. I have two Islands in my house, one is for the kitchen and one is for my wet
bar in another room. They both have a receptacle within 6’ of the sink
installed on the back side of the island. The inspector is requiring that the one
for the wet bar be GFCI protected and not requiring that for the kitchen. Is
that a proper interpretation of the 2011 NEC?
Reference:
NEC 210.8 (A)(6)(7)
Answer: It depends on the placement of the island outlet in the
kitchen area. If the outlet is located low and is NOT intended to serve the
countertop surfaces the inspectors interpretation is correct per 210.8(A)(6).
The island outlet for the other wet bar must be GFCI protected per
210.8(A)(7).
Question #59
Commercial Garages
• Can PVC conduit be installed under the floor of a Commercial
Garage (NEC 511) and if so with what restrictions?
Question #59
Commercial Garage
Answer: Yes.
In 511.4 (A) Wiring and Equipment in Class I Locations shall conform to the
applicable provisions Art 501.
501.10 Wiring Methods (A) (1) (a) Exception; Type PVC conduit and type RTRC
conduit shall be permitted where encased in a concrete envelope a minimum
of (2 in.) thick and provided with not less than (24 in.) of cover measured from
the top of the conduit to grade. Where this exception is used, threaded rigid
metal conduit or threaded steel intermediate metal conduit shall be used for
the last (2ft) of the underground run to emergence or to the point of
connection to the aboveground raceways, and a equipment grounding
conductor shall be included to provided electrical continuity of the raceway
system and for grounding of non-current-carrying metal parts
Question #60
Can a service be located beneath the down spout or over flow
scupper of a building?
Answer: No. See NEC 230.54(G).
(G) Arranged That Water Will Not Enter Service Raceway or
Equipment. Service-entrance and overhead service conductors
shall be arranged so that water will not enter service raceway or
equipment.
Conductors Withstand Ratings
61. How is it NEC compliant to have a #8 Supply side bonding
jumper and 4-#3cu on the line side of a 100a service
disconnect (which may be one of 6 justifying the large
transformer)being fed from a 500kva 13.2 KV to a 208v utility
transformer? Would any of these conductors hold up in a ground
fault or short circuit situation? Is this an area that requires a
code change?
Conductors Withstand Ratings
Answer - Assuming a transformer impedance of 5 percent and an
unlimited supply the available 3 phase short circuit current at the
transformer is 27,750 Amps. This would be reduced to some
lower value at the service equipment based on the length and
size of the service conductors. For estimating purposes, the
ground fault current imposed on the 8 AWG copper supply side
bonding jumper would be about 33% of the 3-phase value or
about 9000 Amps. The current withstand rating of 8 AWG copper
for 9000 Amps is 2 to 3 cycles and fuses or circuit breakers rated
100 Amps would clear this level of fault in 1 to 2 cycles. The 3
AWG copper conductors would withstand the 27,000 Amps for 2
to 3 cycles so the same would apply to these conductors under
full bolted fault short circuit conditions. This is already covered
by the requirements in 110.9 and 110.10.
Ampacity/Adjustment/Correction/Termination
62. What is the maximum allowable ampacity for (6) 3 AWG THHN copper
current-carrying conductors installed in EMT in an ambient temperature of
110 F. and terminated in 60 C. lugs?
Reference: NEC 110,14(C), 310.16(B)(16) 310.15(B)(2)(a) and (3)(a)
•
•
•
110.14(C) states that we can use the rating of the conductor (THHN is 90 degree)
ampacity for adjustment and correction factors however the final ampacity cannot exceed
the lowest temperature rating of any connected termination. Since the terminations are
60 degree the ampacity is limited to 85 amperes in Table 310.15(B)(16) in the 60 degree
column.
310.15(B)(16) allows 115 amps for a 3 AWG THHN in the 90 degree column.
310.15(3)(a) requires an 80% ampacity adjustment for 6 current carrying conductors. 115
x .80 = 92 amperes.
310.15(B)(2)(a) requires a correction factor of .87 for 110 degree ambient temperature in
the 90 degree column. .87 x 92 = 80 as the maximum allowable ampacity.
80 amps are less than 85 amps therefore meeting the 60 degree requirement of 110.14(C)
Farm Demand Load
63. What is the total demand load in kVA for a farm with a 30 kVA
dwelling, a 10 kVA barn and a 3 kVA storage shed?
Reference:
NEC 220.103 with Table 220.103…
Answer: For farm load calculation on a common electrical service
with a dwelling, Table 220.103 may be used for the farm loads
that are added to the 30 KVA dwelling demand load. The
resulting calculation will be :
30 KVA + (10 KVA x 1.00) + (3.0 x 0.75) =
30+10+2.25 = 42.25 KVA
•Smoke Detector Requirements
64) Do wireless interlocked smoke detectors meet the building code
requirement for interlocking smoke detectors in dwelling units, or must
they be hard wired?
•
Smoke detector requirements are not in the NEC. Placement,
power supply, and interconnection requirements are in the
building code.
•Smoke Detector Requirements
SECTION R314 SMOKE ALARMS
R314.1 Smoke detection and notification. All smoke alarms shall be listed
in accordance with UL 217 and installed in accordance with the provisions
of this code and the household fire warning equipment provisions of NFPA
72.
R314.2 Smoke detection systems. Household fire alarm systems installed in
accordance with NFPA 72 that include smoke alarms, or a combination of
smoke detector and audible notification device installed as required by
this section for smoke alarms, shall be permitted. The household fire
alarm system shall provide the same level of smoke detection and alarm
as required by this section for smoke alarms. Where a household fire
warning system is installed using a combination of smoke detector and
audible notification device(s), it shall become a permanent fixture of the
occupancy and owned by the homeowner. The system shall be monitored
by an approved supervising station and be maintained in accordance with
NFPA 72.
•Smoke Detector Requirements
Exception: Where smoke alarms are provided meeting the requirements
of Section R314.4.
R314.3 Location. Smoke alarms shall be installed in the following locations:
1. In each sleeping room.2. Outside each separate sleeping area in the
immediate vicinity of the bedrooms.3. On each additional story of
the dwelling, including basements and habitable attics but not including
crawl spaces and uninhabitable attics. Indwellings or dwelling units with
split levels and without an intervening door between the adjacent levels, a
smoke alarm installed on the upper level shall suffice for the adjacent
lower level provided that the lower level is less than one full story below
the upper level.
When more than one smoke alarm is required to be installed within an
individual dwelling unit the alarm devices shall be interconnected in such
a manner that the actuation of one alarm will activate all of the alarms in
the individual unit.
•Smoke Detector Requirements
R314.3.1 Alterations, repairs and additions. When alterations, repairs
or additions requiring a permit occur, or when one or more sleeping rooms
are added or created in existing dwellings, the individual dwelling
unit shall be equipped with smoke alarms located as required for
newdwellings.
Exceptions:
1.
Work involving the exterior surfaces of dwellings, such as the
replacement of roofing or siding, or the addition or replacement of
windows or doors, or the addition of a porch or deck, are exempt from
the requirements of this section.
2.
Installation, alteration or repairs of plumbing or mechanical systems
are exempt from the requirements of this section.
•Smoke Detector Requirements
R314.4 Power source. Smoke alarms shall receive their primary power from
the building wiring when such wiring is served from a commercial source,
and when primary power is interrupted, shall receive power from a
battery. Wiring shall be permanent and without a disconnecting switch
other than those required for overcurrent protection. Smoke alarms shall
be interconnected.
Exceptions:
1. Smoke alarms shall be permitted to be battery operated when installed
in buildings without commercial power.
2. Interconnection and hard-wiring of smoke alarms in existing areas shall
not be required where the alterations or repairs do not result in the
removal of interior wall or ceiling finishes exposing the structure, unless
there is an attic, crawl space or basement available which could provide
access for hard wiring and interconnection without the removal of interior
finishes.
Question #65
AFCI Protection
An old interior service panel is used as a junction box. The branch
circuits are extended to a new exterior service panel. Are the
branch circuits identified in NEC 210.12(A) required to be arcfault protected?
Question #65
AFCI Protection
Answer: Yes
210.12 (B) Branch Circuit Extensions or Modifications – Dwelling
Units.
In any areas specified in 210.12(A), where branch-circuit wiring is
modified, replaced, or extended, the branch circuit shall be
protected by one of the following:
(1) A listed combination-type AFCI located at the origin of the
branch circuit.
(2) A listed outlet branch-circuit type AFCI located at the first
receptacle outlet of the existing branch circuit.
Question #66
Is it a violation to install a bollard for protection of a panel which
violates the working clearances while the bollard is in place but
where the nuts can be removed with a simple tool to work on the
panel and have the required clearances while you are servicing
the panel?
Question #66
Answer: The AHJ will have to decide if the bollard and steps to remove it, allow access to the
working space. NEC 110.26(E)(2) recognizes that such protection is required for outdoor
equipment.
NEC 110.26(E)(2) Outdoor. Outdoor electrical equipment shall be installed in suitable enclosures
and shall be protected from accidental contact by unauthorized personnel, or by vehicular traffic,
or by accidental spillage or leakage from piping systems. The working clearance space shall include
the zone described in 110.26(A). No architectural appurtenance or other equipment shall be
located in this zone.
110.26 Spaces About Electrical Equipment. Access and working space shall be provided and
maintained about all
electrical equipment to permit ready and safe operation and maintenance of such equipment.
•Garage PV System
67. A solar photovoltaic system is installed on a detached garage
which has a 30A sub-panel and 3-wire feeder so the grounded
conductor is bonded to the grounding electrode system (ground
rod) at the garage. The PV system is larger than the conductors
can carry for a grid-tie system so the PV grid-tie conductors were
run back to the main structure’s main panel. The PV inverter is
grounded to the grounding electrode system of the detached
garage. Since the garage has only a 3-wire system the grounded
conductor was isolated to avoid a parallel path and the
equipment ground with the PV grid-tie conductors was upsized to
accommodate the two systems. Is this legal?
•Garage PV System
Answer - Maybe. With the feeder from the inverter back to the
main building and service having an equipment grounding
conductor the exception in 250.32(A) is no longer valid. The
connection of the inverter grounding electrode conductor to the
garage grounding electrode would be required by 250.58.
Therefore the neutral in the garage panel would have to be
isolated from the enclosure and the grounding electrode
conductor. The only way the single equipment grounding
conductor can serve both the inverter feeder and the garage
feeder is if it was installed in the same raceway or trench using
250.122(C). If the feeders are in separate raceways then the
neutral would have to be isolated and an equipment grounding
conductor from the service panel to the garage panel would
have to be installed per 250.32(A).
Cords
in lifts
Class
Locations
68. Can car
in a1commercial
garage be wired with cords?
Reference:
Answer:
NEC 511.4 501.140
Not unless there is a reason for flexibility or portability
Luminaire Construction
69. Is a sconce with an open top considered guarded?
Reference:
NEC 100 – Guarded
Answer: No, the open-top sconce would not be considered
“guarded”. While the specific application is not indicated, the
definition of “guarded” in Article 100 requires items to be
“Covered, shielded … or otherwise protected … to remove the
likelihood of approach or contact by persons or objects to a
point of danger.” The open top on the sconce would not meet
that requirement of protection.
•Carbon monoxide Detector Requirements
70) In Colorado, where are carbon monoxide detectors required in a
dwelling unit and must they be 120-volt with battery back-up. Also, are
they required to be interlocked with other interlocked smoke detectors in
a dwelling unit?
•
Carbon monoxide detector requirements are not in the NEC.
Placement, power supply, and interconnection requirements are
in the building code.
•Carbon monoxide Detector Requirements
SECTION R315 CARBON MONOXIDE ALARMS
R315.1 Carbon monoxide alarms. For new construction, an approved
carbon monoxide alarm shall be installed outside of each separate
sleeping area in the immediate vicinity of the bedrooms in dwelling
units within which fuel-fired appliances are installed and in dwelling units
that have attached garages.
R315.2 Where required in existing dwellings. Where work requiring
a permit occurs in existing dwellings that have attached garages or in
existing dwellings within which fuel-fired appliances exist, carbon
monoxide alarms shall be provided in accordance with Section R315.1.
•Carbon monoxide Detector Requirements
R315.3 Alarm requirements. Single station carbon monoxide alarms shall be
listed as complying with UL 2034 and shall be installed in accordance with
this code and the manufacturer's installation instructions.
Question #71
Smoke Alarms
•
What is the minimum distance a smoke detector may be
installed from the door of a bathroom containing a shower in a
dwelling unit?
Question #71
Smoke Alarms
Answer: NEMA Standard SB 11 – 2011 provides general guidance.
“In damp or excessively humid areas, or next to bathrooms with
showers. Tiny droplets can accumulate inside the sensing chamber and
make the detector overly sensitive. A tremendous amount of humid air
is produced during a hot shower. The moisture in this humid air can
enter the sensing chamber as water vapor, then cool and condense into
droplets that can cause a nuisance alarm”.
NFPA 72-2010 and 2013 prohibits a smoke alarm or detector from
being installed within 36 inches from a door leading to a bathroom
containing a shower or tub.
Question #72
Circuit Breakers
Are branch circuit breakers marked “SWD” and rated for 480 volts
suitable for switching fluorescent lighting loads?
Answer: Yes, see NEC 240.83(D).
(D) Used as Switches. Circuit breakers used as switches in 120-volt and
277-volt fluorescent lighting circuits shall be listed and shall be marked
SWD or HID. Circuit breakers used as switches in high-intensity
discharge lighting circuits shall be listed and shall be marked as HID.
UL Whitebook - CIRCUIT BREAKERS, MOLDED CASE AND CIRCUITBREAKER ENCLOSURES (DIVQ) - Circuit breakers marked "SWD" and
rated 347 V or less are suitable for switching fluorescent lighting loads
on a regular basis at their rated voltage.
•Installation of MRI Equipment
73. Manufactures of MRI machines have been adamant about
there not being any metallic pathways out of the MRI room that
could cause interference with the imaging. They spec an
isolation coupling in the conduit of the branch circuits into the
room. How are inspectors supposed to deal with this issue in
regards to 517.13?
•Installation of MRI Equipment
Answer - The only circuits that should be going into the
shielded MRI room are those directly related to the MRI
equipment. Generally all the MRI circuits go through a special
isolation panel in the wall of the special room to shield any
outside coupling that could create interference to the
magnetic imaging equipment as well as any of the magnetic
energy to leave the room. Lighting circuits in the ceiling should
be higher than where these would fall under 517.13. If the
circuits are those related to the MRI equipment assembly
directly, that equipment is covered under its listing and these
are not building construction circuits that would be subject to
517.13 just as internal wiring in other medical equipment in a
patient care area are not subject to this provision. That listing
includes specific provisions for assurance of equipment
grounding to the single point grounding reference to assure
proper operation of the MRI equipment.
Wet
Location
Weather-Resistant
Receptacle?
74.
A low
volt panel/installed
outside has a receptacle
inside; does
this receptacle need to be WR
Reference:
406.9(B)(1)
Answer: Yes, 15- and 20-ampere, 125- and 250-volt receptacles
installed in a wet location shall have an enclosure that is
weatherproof whether or not the attachment plug cap is
inserted. All 15- and 20-ampere, 125- and 250-volt nonlockingtype receptacles shall be listed weather-resistant type.
Range Demand Load
75. What is the demand load for (20) 8 kW ranges installed in a
multi-family dwelling?
Reference:
NEC 220.55 with Table 250.55.
Answer:
Use of Column C in Table 220.55 is to be utilized for determination
of loads. Note 3 permits exception primarily for loads on
multiple cooking units within dwelling units. The demand load
for 20 ranges rated at 8 KW is 35 KW as indicated in Column C.
•Equipotential bonding in livestock containment areas.
76) Are the stock holding pens (with concrete floors)
of a slaughter house facility required to have the
equipotential plane bonded? There are stock tank
heaters in the pens and chutes. The rails and posts
are steel.
Article 547.10 (A)(B)
As there are electrical devices and concrete floors in the livestock
containment area equipotential plane bonding is required.
Minimum 8 AWG SOLID conductor required.
Question #77
Barriers
Answer: 300.3(C) (1) Conductors of Different Systems.
(1) 600 Volts, Nominal, or less. Conductors of ac and dc circuits,
rated 600 volts, nominal or less shall be permitted to occupy
the same equipment wiring enclosure, cable, or raceway. All
conductors shall have an insulation rating equal to at least the
maximum circuit voltage applied to any conductor within the
enclosure, cable, or raceway.
Informational Note #1: See 725.136(A) for class 2 and Class 3
circuits conductors.
Question #77
Barriers
Answer Continued:
Art. 725.136(A) Separation from Electric Light, Power, Class 1
ect.
(A) General: Cables and conductors of Class 2 and Class 3 circuits
shall not be placed in any cable, cable tray, compartment,
enclosure, manhole, outlet box, raceway, or similar fitting with
conductors of electric light, power, Class 1, non-powered
broadband communications circuits unless permitted by
725.136(B) through (I).
Question #77
Barriers
Answer continued:
Art. 725.136(B) Separated by Barriers.
Class 2 and Class 3 circuits shall be permitted to be installed
together with the conductors of electric light, power, Class 1,
non-power-limited fire alarm and medium power networkpowered broadband communications circuits where they are
separated by a barrier.
Question #78
690.14 states that the ac disconnect is not required to be suitable
for service equipment. Would the AC disconnect for a line side
tap be required to be suitable for service equipment?
Answer: No. SUSE is not required.
If this is a utility interactive application the requirements for the
point of connection are found in NEC 690.64. In the 2011 NEC,
these requirements were appropriately moved to Article 705
such that NEC 690.64 simply sends you to NEC 705.12.
Question #78
Answer Continued:
690.64 Point of Connection. Point of connection shall be in
accordance with 705.12.
705.12(A) Supply Side. An electric power production source shall
be permitted to be connected to the supply side of the service
disconnecting means as permitted in 230.82(6). The sum of the
ratings of all overcurrent devices connected to power production
sources shall not exceed the rating of the service.
Also see 705.20,21.22 for the disconnect requirements – SUSE is
not a requirement.
•Transformer Feeder Installation
79. We have a facility that owns the 13k step down to 208v
transformer that is normally owned by the utility. The
transformer is located in the basement of the building in a
retirement center. With fault currents over 30k, Is it legal to use
the 25’ tap rule per 240.21(C)( 6) and run EMT over head to the
208v MDP or should these secondary conductors be treated as
service conductors and installed to be outside the building by a
permitted method?
•Transformer Feeder Installation
Answer - The transformer as described as owned by the facility would
mean this is a separately derived system and that there is a service to
the facility at 13KV with all related service equipment. The wiring from
the transformer to the 208 Volt MDP is a feeder and the various feeder
tap rules in 240.21(C) would be applicable. These conductors would
have short circuit and high level ground-fault protecting provided by
the primary protections device. The overload protection is provided by
the secondary overcurrent device(s). Being in the basement, I am
assuming this is not a vault that would be considered outside the
building. So, with these assumptions the transformer secondary
conductor rules for 10 foot, 25 foot etc. distances would could be
applied depending on meeting the specific requirements for each of
the allowed installations. This feeder could be installed in EMT from
the basement to the MDP following the proper wiring methods from
Chapter 3.
Selection of Ampacity
80. What is the ampacity of (8) 6 AWG THHN copper current-carrying
conductors installed in EMT that have a total length of 75 feet, but of
which 8 feet pass through a boiler room with an ambient temperature of
120 F.?
Reference: NEC 310.15(A)(2) 310.(B)(16) 310.15(B)(2)(a) and (3)(a), 110.14(C)
Answer: We can start the calculation using the rating of the conductor according to 110,14.
•
•
310.15(B)(16) allows 75 amps for a # 6 THHN in the 90 degree column. 310.15(B)(3)(a)
requires an 80% adjustment factor for 8 current-carrying conductors. 80% of 75 = 60
amps.
310,15(A)(2) States; Where more than one ampacity applies for a given circuit length,
the lowest value shall be used. Because 10 ft. or 10% of the circuit runs through 120
degree boiler room a correction factor of 82% is required from 310.15(B)(2)(a)
60 x .82 = 49 amperes allowed. This does not exceed the 60 degree ampacity of 55
amperes meeting the requirements of 110.14(C).
Water Heater Circuit
81. What is the minimum size branch circuit allowed for a 4500
watt, 240-volt, 40 gallon water heater?
Reference:
NEC 422.13, 210.19(A), and 240.4(D)(7)
Answer: Under NEC 422.13, storage type electric water heaters
are to be considered continuous loads with a resulting
demand factor of 1.25 for sizing branch circuits per 210.19(A).
Using the unit element size of 4,500 watts (volt-amperes) at
240 volt, 1-phase, the calculated demand load is:
(4,500 x 1.25) / 240 = 5,625 / 240 = 23.4; rounded to 23 amperes
Using NEC 240.4(D)(7), the #10 AWG minimum conductor size
would be selected with overcurrent protection at 30 amperes.
•Use of NM-B cables in barns.
82) Is NM-B cable allowed to be used in any area of a
barn?
Article 547.1
The provisions of this article shall apply to the following buildings
or that part of a building or adjacent areas of similar or like
nature as specified in 547.1(A) or (B).
There are may be some areas of a barn where NM-B is acceptable
for use. Where NM-B is installed the requirements of Article
334 must be used.
Question #83
Information Technology Equipment
•
Can a field installed receptacles and wiring methods be
considered “listed for information technology equipment” per
645.5G (B) to not have to secure and support under the raised
floor? What would be an example of where you have to secure
& where you do not have to secure receptacles and wiring
methods from a PDU under a floor?
Question #83
Information Technology Equipment
Answer: NO.
645.5(E) Branch-circuit conductors installed under the raised floor of an
ITE room using any of the wiring methods listed in 645.5(E)(2) are
required to conform to the specific article for the wiring method used.
In addition, Article 300 applies, except where modified by Article 645.
For example, 300.11 requires raceways, cables, and boxes to be
securely fastened in place, even though they are installed below a
raised floor.
645.5(F) Securing in Place. Power cables; communications cables;
connecting cables; interconnecting cables; and associated boxes,
connectors, plugs, and receptacles that are listed as part of, or for,
information technology equipment shall not be required to be secured
in place.
Question #84
For a 120v phase to phase isolated power system supplying
receptacles in a hospital operating room. Is it required to install
bonding bushings or bonding locknuts on the EMT entries to the
4 square boxes or is a standard locknut sufficient?
Answer: Yes, bonding bushing or bonding locknuts are required.
NEC Article 358 permits EMT to be used as an equipment
grounding conductor when installed as a system and appropriate
fittings are used. Article 517.13(A)/(B) set the requirements for
using a metal raceway system which qualifies as an equipment
grounding conductor and an insulated equipment grounding
conductor to the receptacle/box.
Question #84
Answered Continued:
517.19(D) Equipment Grounding and Bonding. Where a grounded
electrical distribution system is used and metal feeder raceway or
Type MC or MI cable that qualifies as an equipment grounding
conductor in accordance with 250.118 is installed, grounding of
enclosures and equipment, such as panelboards and switchboards,
shall be ensured by one of the following bonding means at each
termination or junction point of the metal raceway or Type MC or
MI cable:
(1) A grounding bushing and a continuous copper bonding jumper,
sized in accordance with 250.122, with the bonding jumper
connected to the junction enclosure or
•Fault Current Limiting
85. Is it NEC compliant per 110.3 to reduce the fault current by
using let through current “up over down method” to protect a
standard breaker panel? Is this an approved method per UL ?
•Fault Current Limiting
Answer - No. The short circuit current available at the line
terminals cannot exceed the Short Circuit Current Rating of the
panel. Where the quick calculation shows a possible Short
Circuit Current higher than the rating, then a more detailed short
circuit study or calculation needs to be done to include all wire
impedances and the true available current at the supply
transformer. If the fault current calculated still exceeds the
rating of the panel, then either the panel will need to be
replaced with one with suitable ratings or some other means,
such as inserting an impedance, to reduce the flow through fault
current. A current limiting fuse using the up-over-down method
is not an acceptable alternative.
Splices
in LB?
86. How many
#14 wires can I splice in a ¾” LB that is labeled with 6.5
cubic inches?
Reference: NEC 314.16(C)(2) Conduit Bodies With Splices, Taps, or
Devices. 314.14(B)
Answer: Only those conduit bodies that are durably and legibly marked
by the manufacturer with their volume shall be permitted to contain
splices, taps, or devices. The maximum number of conductors shall
be calculated in accordance with Table 314.16(B).
Table 314.16(B), shows a 14 AWG as being 2.00 cubic in. The LB is 6.5
cubic inches divided by 2.00 = 3 # 14 AWG allowed, 2 that are spliced
and one passing through.
Office Demand Load
87. What is the lighting load in VA for a 10,000 sq. ft. office
building, including general purpose receptacles, where the
number of general purpose receptacles is unknown?
Reference:
NEC 220.12, Table 220.12, and 220.14(K)
Answer: The minimum General Lighting Load for an office facility
is designated in Table 220.12 as 3.5 volt-amperes (VA) per
square foot (VA/SF). In addition, the general receptacle load
where not available from 240(I) is designated as 1.0 VA/SF in
240.14(K). The calculation for combined general lighting and
receptacle loads is:
10,000 x (3.5 + 1.0) = 10,000 x 4.5 = 45,000 VA
•Protection from physical damage.
88) Does the code specify protection from damage
requirements or does the authority having jurisdiction make
his own requirements [ as for NEC 110.26 [E]
The AHJ always has the last say. That said there are a few areas in
the code where physical protect is required such as Article
334.15 (B), (C).
Question #89
Conduit Bodies
What kind of devices are allowed in a conduit body (referred to in
314.16(C)(2)?
Answer: There is not a conduit body made with a mounting yoke
inside it. When 314.16(C)(2) mentions devices, they refer to all
electrical devices. As you recall an electrical device is a device
that either produces, consumes, or directs (receptacles)
electricity. Some would even say a wire nut is a device.
Question #90
Is it required to install a disconnecting means on each light pole
since it is defined as a structure by the code making panel?
Answer: No, see NEC 225.32 Exception No. 3
225.32 Exception No. 3: For towers or poles used as lighting
standards, the disconnecting means shall be permitted to be
located elsewhere on the premises.
•Rebar Connections
91. Since rebar can simply be tie wired together and this is
approved for the UFER. Can a CU conductor simply be tie wired
to the rebar?
•Rebar Connections
Answer - No. 250.70 requires the connection of the grounding
electrode conductor to the grounding electrode using
exothermic welding or a suitably listed lugs, listed pressure
connectors, listed clamps, or other listed means. For a
connection device to be embedded in concrete it must also be
listed and identified for direct burial and/or concrete
encasement. Listed devices suitable for connection of grounding
electrode conductors can be found under UL Category Code
KDER on page 217 of the 2012 UL White Book. Tie wires are not
a listed device nor specifically allowed by 250.70.
Corner
Grounded
Delta
Grounded
Phase?leg
92. On a “corner
grounded
delta”/service,
is the grounded
required to be in the “A”, “B” or “C” phase location?
Reference: Schneider-Electric - Definitions
Answer: Corner-Grounded Delta System A system in which the
transformer secondary is delta-connected with one
•
corner of the delta solidly grounded. Corner-grounded delta
systems are also referred to as grounded B phase systems,
grounded phase services, and end-grounded delta systems
Ground Ring Electrode
93. What is the minimum size copper grounding electrode conductor
allowed to connect to a ground ring?
Reference:
NEC 250.52(A)(4) and 250.66(C)
Answer: The minimum size of a ground ring encircling a building or
structure shall be #2 AWG per NEC 250.52(A)(4). The minimum
size for the bare copper grounding electrode conductor is
established in NEC 250.66 as the values shown in Table 250.66,
except as permitted in paragraphs 250.(A), (B), and (C). The
grounding electrode conductor under 250.66(C) is allowed to be the
same size of the conductor for the ground ring or thus #2 AWG,
(unless a larger ground ring is installed).
•Outlet spacing/wall spaces.
94) Is a receptacle on 24” wall located behind the swing of a door required?
Article 210.52(A)(2)(1)
Yes an outlet is required on the wall space.
Any space 2 feet or more in width and unbroken along the floor
line by doorways and similar openings, fireplaces, and fixed
cabinets.
Question #95
Conduit Bodies
What length of a “C” Conduit body is required for #4 wire pulled in a 2” conduit?
Answer: 314.28 Pull and Junction Boxes and Conduit Bodies.
Boxes and conduit bodies used as pull or junction boxes shall comply with 314.28(A) through
(E).
•
(A) Minimum Size. For raceways containing conductors of 4 AWG or larger that are
required to be insulated, and for cables containing conductors of 4 AWG or larger, the
minimum dimensions of pull or junction boxes installed in a raceway or cable run shall
comply with (A)(1) through (A)(3). Where an enclosure dimension is to be calculated based
on the diameter of entering raceways, the diameter shall be the metric designator (trade
size) expressed in the units of measurement employed.
•
(1) Straight Pulls. In straight pulls, the length of the box or conduit body shall not be less
than eight times the metric designator (trade size) of the largest raceway.
Question #96
I have a 200A service on a residence fed with 4/0 aluminum and a 100A sub panel. What size
SER cable do I need to run to the sub panel?
The requirements for using SE type cable for feeder and branch circuit wiring are found in
NEC Article 338. In particular to this question, NEC 338.10(B)(4)(a) covers indoor
installations of this cable and includes requirements for cases where the cable is installed in
thermal insulation. See the second paragraph from this section below:
Where installed in thermal insulation, the ampacity shall be in accordance with the 60°C
(140°F) conductor temperature rating. The maximum conductor temperature rating shall be
permitted to be used for ampacity adjustment and correction purposes, if the final derated
ampacity does not exceed that for a 60°C (140°F) rated conductor.
Question #96
Answered Continued: Since this installation does not qualify as a main power
feeder per NEC 310.15(B)(7), use of the table 310.15(B)(7) is not permitted and all
of the requirements of NEC 310.15 will apply in sizing the SER cable for this
installation.
Case 1: SER installed in thermal insulation, 40 C ambient. From Table
310.15(B)(16), using 60 C column, a #1 Cu or 1/0 Al size would be the minimum
size required but we must check for any adjustment or correction factors.
Checking for ambient adjustment, Table 310.15(B)(2)(a) requires a 0.91 adjustment
for 40 C ambient. Since SER cable has a temperature rating of 90 C we can use that
column from table 310.15(B)(16) so 145 A X 0.91 = 132A Cu and 135 x 0.91 = 123 A
Al.
#1 CU or 1/0 AL is required for this feeder.
Question #96
Answered Continued:
Case 2: SER NOT installed in thermal insulation, 40 C ambient.
SER cable is listed as an assembly for 75 C so from Table
310.15(B)(16), a #3 Cu or #1 Al size would be the minimum size
required but we must check for any adjustment or correction
factors. For the adjustment and correction factors, the
temperature rating of the conductors can be used, 90C.
Checking for ambient adjustment, Table 310.15(B)(2)(a) requires
a 0.91 adjustment for 40 C ambient. Using the 90 C column from
table 310.15(B)(16) so # 3 Cu - 115 A X 0.91 = 105A and #1 Al 115 x 0.91 = 105 A.
#3 CU or #1 AL is required for this feeder.
•Structural Steel Grounding Electrode
97. We have a precast building that has multiple areas,
separated by the precast, containing a steel framework of beams
and bar joists. The building has a 2/0 counterpoise ground
system surrounding it in a ring with multiple ground rods. The
lightning protection system is bonded many times to this ground,
as well as the main service grounding electrode system. Building
steel in each of these separate areas is also bonded to the
counterpoise ground. Can the building steel be considered a
grounding electrode and be used to bond the separately derived
system transformers without having to run all the way back to
the main service?
•Structural Steel Grounding Electrode
Answer - The building steel would be considered a grounding
electrode conductor or common grounding electrode conductor
per 250.68(C). Since the building steel is bonded to the overall
grounding electrode system, then it would qualify and be
suitable for use to ground the separately derived systems.
NM
Cable / 60 or 90 degree?
• 98. When the sheathing is removed from NM cable, can you treat the
individual conductors as THWN or is it still NM cable?
Reference:
NEC 334.80 Ampacity
Answer: It’s still NM cable; the conductors are unmarked and would be
rated for 60 degree..
• The ampacity of Types NM, NMC, and NMS cable shall be determined
in accordance with 310.15.
• The allowable ampacity shall not exceed that of a 60°C (140°F) rated
conductor. The 90°C (194°F) rating shall be permitted to be used for
ampacity adjustment and correction calculations, provided the final
derated ampacity does not exceed that of a 60°C (140°F) rated
conductor
Fault Current Rating
99. On an existing commercial building a portion of the tenant space
is being remodeled. During a rough electrical inspection, the service
is looked at and the breakers do not have a high enough AIC rating for
the available fault current. Can the inspector require the service or
any of the panels being used
Reference:
NEC 90.4, 110.10, 110.22, and 110.24
Answer: Under the provisions of NEC 110.10, 110.22, and 110.24, the
design and application of individual system components is to be
provided as needed to withstand the affects of short circuit
current under fault conditions. Where an existing installation is
found deficient or improperly installed, the Authority Having
Jurisdiction (AHJ) has the responsibility of enforcement and
determination of approval of equipment and materials, as defined
in NEC 90.4. In this case, the extent and depth of such action that
is required is at the discretion of the AHJ.
•Carbon monoxide Detector Requirements
100) In Colorado, where are carbon monoxide detectors required in a
dwelling unit and must they be 120-volt with battery back-up. Also, are
they required to be interlocked with other interlocked smoke detectors in
a dwelling unit?
•
Carbon monoxide detector requirements are not in the NEC.
Placement, power supply, and interconnection requirements are
in the building code.